In recent years, due to the rapid development of industrialization, discharge of a large amount of industrial waste water from mining, smelting, coal-burning, papermaking, etc has caused a drastic increase in heavy metal pollutants in soil of China. Due to heavy metals cannot be degraded by microorganisms, it is difficult to be eliminated, and accumulation of these metals to a certain extent in soil can cause toxicity to soil plant system, these result in degradation of soil quality and reduction in crop yield and quality. In China, grain production is decreased as high as 10 million tons every year due to soil heavy metal pollution, and there are 12 million tons of grains having the content of heavy metals above the national standards. More importantly, heavy metals may be also migrated to animals and humans through food chain, severely endangering animal and human health and affecting ecological environment security.
At present, an idea for treating heavy metal pollution in soil has been changed from complete removal of heavy metals to implementation of risk-based control strategies. The indicator that truly affects soil risk is the bioavailability of heavy metals. Therefore, reducing the bioavailability of heavy metals is one of the effective ways to control heavy metal polluted soil. In-situ passivation of heavy metals in soil is to change the form of heavy metals in the soil by adding passivator to heavy metal polluted soils, mainly aiming to convert exchangeable and carbonate bound forms of heavy metals with high bioavailability to organic bound and residual forms of the heavy metals with low bioavailability. This technology has been widely concerned because of its short processing time, simple operation, quick response, and suitability for large-area pollution treatment.
A key to the in-situ passivation of heavy metals in soil is the preparation and use of passivator. Currently, commonly used passivators are mainly classified into inorganic, organic, microbial, and novel composite materials. In practical soil environment, heavy metal pollution is mostly combined pollution of two or more elements, and common defects of the first three types of single material are that types of pollutants treated are also relatively monotonous, and limitations are relatively large, so the combined pollution in soil is poorly treated. Therefore, focusing on all types of environmental materials and their combined use, and developing new composite materials through chemical synthesis, modification, composting, etc. are main directions for future development of the in-situ passivation of heavy metals in soil.